1. Field of the Art
This invention relates to a novel monoclonal antibody having specificity to an isozyme of cardiac myosin heavy chain.
In recent years, as a method for obtaining an antibody having high specificity in a large amount, it has been known to prepare a hybridoma, by fusion of an antibody-producing cell with a myeloma cell and culturing the hybridoma thus obtained to produce a monoclonal antibody (Kohler et al, Nature, Vol. 256, p. 495 (1975)), and a large number of monoclonal antibodies have been obtained by such a method.
2. Prior Art
In the field of muscle research, antibodies against muscle proteins have long been utilized. Muscles are classified broadly into the two groups of striated muscles and smooth muscles. Striated muscles are further classified into cardiac muscles and skeletal muscles, the skeletal muscles being further cllassified into fast muscles and slow muscles. It has been reported that these can be distinguished immunochemically through the difference in immunogenicity of the myosin molecules which are major constituents of muscles (Masaki et al: J. Biochem. Vol. 76, p. 441 (1974)).
Recently, concerning also cardiac muscles, the existence of two isozymes, one being V.sub.1 (.alpha. type) having a high ATPase activity and the other being V.sub.3 (.beta. type) having a low ATPase activity (Yazaki et al: Circulation Research, Vol. 35 p. 15 (1974); Hoh et al: J. Mol. Cell. Cardiol. Vol. 10, p. 1053 (1978)) has become apparent. Generally speaking, in animals such as humans, bovines, canines and others, atrial muscles contain primarily V.sub.1 (.alpha. type), while ventricular muscles contain substantially V.sub.3 (.beta. type). Accordingly, if it is possible to prepare monoclonal antibodies specific for .alpha. type or .beta. type myosin, the atrial muscle and the ventricular muscle could be stained specifically by a method such as a biotin-avidin system. Further, these antibodies can be labelled with radioisotopes and used for localization of myocardial infarction.
W. A. Clark et al immunized mice and rats with chicken or rabbit cardiac myosin and obtained monoclonal antibodies which reacted with cardiac myosin heavy chain (Biochem. Biophys. Res. Commun. Vol. 95, p. 1680). They reported that one clone of those obtained is specific for chicken cardiac muscle and does not react with human cardiac muscle. Other two clones react with cardiac muscles of chickens, rabbits and rats, and also with human cardiac muscle, but they are also reactive with skeletal muscles and therefore not specific for cardiac muscles. These antibodies would not recognize human cardiac myosin of .alpha. type over .beta. type or vice versa.
Further, W. A. Clark et al immunized mice with chicken cardiac myosin or rabbit cardiac myosin and obtained monoclonal antibodies to cardiac myosin heavy chain V.sub.1 type and cardiac myosin heavy chain V.sub.3 type (J. Biol. Chem., Vol. 257, p. 5449 (1982)). However, these antibodies are shown to exhibit also cross reactivity mutually between the isozymes thereof, and nothing appears to be shown in about their specificity to human cardiac myosin.